In order to crack down on people taking advantage of currency differences around the world, Valve has begun blocking game gifting and trading between certain regions. This is also thought to be an effort to help prevent money laundering through people using stolen money and credit cards to buy games, which they can then sell on for clean money elsewhere in the world.
None of the affected regions are Western. In-fact, Europe, the US, Canada, Australia, New Zealand and a number of other territories are unaffected. However, Eastern Asian nations like Singapore, Malaysia, Indonesia, Thailand and Vietnam can only trade with one another. Turkey can only gift games to other Turkish accounts, Russia can only trade with itself and the Commonwealth of Independent States (ex-soviet countries) and South America and Mexico can only trade with one another too.
While Valve hasn't made this an official announcement, it's clear from notices appearing when people buy games in different territories that they are preventing trading from happening across the globe.
This could well mean the end for cheap CD-key sites, which have previously relied on stolen keys and cards being used, as well as overseas trading where prices are more favourable.
Will this change in policy affect you guys at all?